PREPARATIONS Required: Mannitol, 5 g.; acetic anhydride, 30 ml.; zinc chloride, ca. 0-5 g. Add 5 g. of finely powdered mannitol to 30 ml. of acetic anhydride contained in a ioo ml. round-bottomed or conical flask. Now break off a small fragment (not exceeding 0-5 g.) from a clean dry stick of zinc chloride, crush it quickly into coarse fragments in a mortar, and then add it to the acetic anhydride: this manipulation of the zinc chloride—as in the above preparation of a-pentacetyl-glucose—should be performed as rapidly as possible. (Alternatively, 4 g. of powdered anhydrous sodium acetate may be added in place of the zinc chloride.) Boil the mixture gently on a sand-bath under a reflux water-condenser for 30 minutes, a clear solution being rapidly obtained. Then pour the solution into 250 ml. of cold water, stirring the mixture vigorously for a few minutes until the oil which separates at first has solidified to a mass of fine colourless crystals. Allow to stand for 15 minutes, and then filter at the pump, wash thoroughly with
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